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Date: Tue, 9 Sep 2008 10:43:25 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Joe Peterson <joe@skyrush.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] TTY: Fix loss of echoed characters (2nd follow-on PATCH
 attached)
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On Tue, 9 Sep 2008 11:55:36 +0100 Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

> On Mon, 8 Sep 2008 17:32:50 -0700
> Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > On Mon, 08 Sep 2008 10:11:46 -0600
> > Joe Peterson <joe@skyrush.com> wrote:
> > 
> > > +	spin_lock_irqsave(&tty->echo_lock, flags);
> > >  	lock_kernel();
> > 
> > Taking a spinlock outside lock_kernel() isn't good, and is quite unusual.
> > 
> > - It might be ab/ba deadlockable (I didn't check) (I trust you always
> >   test with lockdep enabled?)
> 
> lock_kernel can sleep.

That used to be the case, but the mutex_lock() version of the bkl got
removed.  It may of course come back.

> Its not allowed...
> 

yup.